A high frequency switching circuit is a important constituent part for a radio communication system such as a mobile communication or a LAN system. Lots of high frequency switching circuits are used in mobile phones, radio infrastructure facilities, satellite communication facilities or cable television facilities.
A high frequency switching circuit is disclosed in U.S. Pat. No. 6,094,088, for example.
The high frequency switching circuit mentioned in the United States patent is provided with a pair of FETs (Field Effect Transistors) called as “Through FETs” and a pair of FETs called as “Shunt FETs”, which are used to switch two higher frequency input signals selectively. The high frequency switching circuit has capacitances respectively between the gate and the drain, between the back-gate and the drain, between the gate and the source and between the back-gate and the source, with respect to each of the Through FETs.
Further, the high frequency switching circuit has capacitances respectively between the gate and the drain, between the back-gate and the drain, between the gate and the source and between the back-gate and the source, with respect to each of the Shunt FETs.
The gates and back-gates of the Through FETs and Shunt FETs connect with resistors respectively. These resistors serve to suppress leakage of higher frequency signal when any selected one of the Through FETs and any selected one of the Shunt FETs are in an ON state.
However, there is a problem that, when any selected one of the Through FETs and any selected one of Shunt FETs are in an OFF state, high frequency signal supplied from the drain sides leaks to the source sides via the capacitances due to existence of the resistors.
The leakage of the higher frequency signal from the drain sides to the source sides causes lowering isolation characteristics of the Through FETs and the Shunt FETs in the OFF state so that the high frequency switching characteristic lowers.